1. Field of the Invention
The present invention relates to a wire sawing apparatus whose linear wire is caused to reciprocate in its own linear direction and to cut into an object to be cut to thereby cut the object, as well as to a wire sawing method using the wire saw.
2. Description of the Related Art
In recent years, a piezoelectric/electrostrictive device has been developed as an actuator for precision working; as an actuator for controlling the position of a read and/or write element (head) for reading and/or writing optical information, magnetic information, or like information; as a sensor for converting mechanical vibration to an electrical signal; or as a like device. The piezoelectric/electrostrictive device includes a stationary portion, a thin-plate portion supported by the stationary portion, and a piezoelectric/electrostrictive element including laminar electrodes and piezoelectric/electrostrictive layers.
FIG. 38 shows an example of such a piezoelectric/electrostrictive device, which is disclosed in Japanese Patent Application Laid-Open (kokai) No. 2001-320103. The piezoelectric/electrostrictive device includes a stationary portion 100; thin-plate portions 110 supported by the stationary portion 100; holding portions (movable portions) 120 provided at corresponding tip ends of the thin-plate portions 110 and adapted to hold an object; and piezoelectric/electrostrictive elements 130 formed at least on corresponding planes of the thin-plate portions 110, each piezoelectric/electrostrictive element 130 including a plurality of electrodes and a plurality of piezoelectric/electrostrictive layers arranged alternatingly in layers. An electric field is generated between electrodes of the piezoelectric/electrostrictive elements 130 so that the piezoelectric/electrostrictive layers of the piezoelectric/electrostrictive elements 130 extend and contract, whereby the thin-plate portions 110 are deformed. The deformation of the thin-plate portions 110 causes displacement of the holding portions 120 (accordingly, displacement of the object held by the holding portions 120).
The piezoelectric/electrostrictive device of FIG. 38 is manufactured as follows. First, as shown in FIG. 39, a plurality of ceramic green sheets (and/or a ceramic green sheet laminate) are prepared. As shown in FIG. 40, these ceramic green sheets are laminated and then fired, thereby forming a ceramic laminate 200. As shown in FIG. 41, piezoelectric/electrostrictive laminates 210 each including a plurality of electrodes and a plurality of piezoelectric/electrostrictive layers arranged alternatingly in layers are formed on the surface of the ceramic laminate 200. A monolithic body consisting of the ceramic laminate 200 and the piezoelectric/electrostrictive laminates 210 (the monolithic body being an object to be cut) is cut along cutting lines C1 to C4 shown in FIG. 42, thereby yielding the piezoelectric/electrostrictive device.
Such cutting can be performed by mechanical machining, such as wire sawing or dicing, as well as laser machining, such as YAG laser machining, excimer laser machining, or electron beam machining. Cutting the ceramic laminate 200 and the piezoelectric/electrostrictive laminates 210 along the cutting lines C3 and C4 includes cutting of the components of the piezoelectric/electrostrictive laminates 210; i.e., cutting of piezoelectric/electrostrictive layers which are relatively low in strength and fragile, and a metal which is ductile. Thus, machining (e.g., dicing) that imposes a large machining load on an object to be cut is undesirable. Machining of another type (e.g., wire sawing) that imposes a small machining load on an object to be cut is desirable.
In the above-described piezoelectric/electrostrictive device, the relationship between the displacement of an object held between the holding portion 120 and the intensity of electric field generated between the electrodes (i.e., an operating characteristic of the piezoelectric/electrostrictive device) must be of very high accuracy. The relationship between the displacement of the object and the electric field intensity depends greatly on the shape (geometric accuracy) of the piezoelectric/electrostrictive device (particularly, the thin-plate portions 110). Accordingly, when wire sawing is applied to cutting along the cutting lines C3 and C4, wire sawing must be performed at very high accuracy.